See post #25 in this thread, the guy lives in a cool and low humidity location.
Bad powder at such young age
https://www.thehighroad.org/index.php?threads/bad-powder-at-such-young-age.840053/
Ionic compounds hasten the deterioration of gunpowder by interacting with the double bonds in nitrocellulose. Water is polar covalent, is a weird and miraculous compound, without which life on this planet would not exist if not for its screw ball properties. Water acts ionic due to the distribution of charge on the molecule, and as such, condensation and evaporation of humidity in air, which is going on all the time, will break down gunpowder. That is also why you should not pour a can of iron filings, or rust, into your gunpowder, or pour anything else that will react with the NO double bonds. Hence, the warning about dry.
Understand this, gunpowder is a high energy compound breaking down to a low energy compound and it is breaking down from the day it leaves the factory. It is not going to be immortal in a vacuum pack. Heat is the primary enemy of gunpowder. Heat deteriorates gunpowder, and it is an exponential deterioration. The hotter it is, the faster the gunpowder deteriorates.
Heat is used to accelerate deterioration, and ammunition stockpiles are tested, typically at 165 F, to see how long it takes for the gunpowder to fume. If it fumes within 30 days, it is withdrawn from inventory. This is a 1970 chart, but worth looking at.
This is not a simple issue and there are books and chapters addressing this:
So, in general, keep your ammunition and gunpowder cool and dry. Inspect at reasonable intervals. Break the seals on your gunpowder and sniff.
If your ammunition starts blowing primers or cracking case necks, pull the bullets and dump the powder. The gunpowder is outgassing and having burn rate instability.
Similar to the advice of eating right and exercising, and not smoking, there is little more you can do to extend the shelf life of your gunpowder. But, unpredictable things happen. I knew a guy who never smoked, never drank, ate right, and in his 40's died of a heart attack on the jogging track. Bummer, do every thing right and you still end up just as dead as that bug on your windshield. Same can happen to your gunpowder. You can do everything right, and your gunpowder may burst into flame and burn your house down.
Prudent thing to do, inspect, shoot the oldest stuff up, and blow it all down range before gets to be 20 years old. I picked twenty because I am been tossing Accurate Arms AA4064, Vihtavouri N140, and N135 that are all around 20 years old. It can go bad earlier, but, gunpowder really goes down hill around 20 years of age.
The guys who posted these pictures of their WW2 era gunpowder hoards, they think by not breaking the seal, their hoard will last forever. Oops, wrong!
They will be lucky if they wake up with their house in flames. It is more likely they will die in their sleep, when their house bursts into flames.
While auto combusting gunpowder did not kill the Norris family, a kerosene heater did, none of them apparently woke up when their trailer caught on fire.
Who is not showing is Grand Dad. Grand Dad died trying to pull his grand kids and daughter in law out of the burning trailer. He did not make it. Son was not there at the time, can only guess what happened a year later. Someone still grieves over the loss.